A heat pipe is a closed-loop, cooling device wherein heat is transferred from the xe2x80x98evaporatorxe2x80x99-end to the xe2x80x98condenserxe2x80x99-end of a sealed tube using the latent heat of vaporization as the principal means of energy transfer. A heat-pipe consists of three principal elements: 1) a sealed tube (typically copper), 2) a heat-transfer medium (such as water, ammonia, or methanol) enclosed under partial vacuum (or pressurized in some cases) within the tube, and 3) an internal xe2x80x98wickxe2x80x99 structure. The addition of heat to the evaporator end of the tube vaporizes the liquid heat-transfer medium, which is transported by vapor pressure to the condenser end. Upon collision with the cooler surfaces of the condenser, the vapor condenses, and is transferred by capillary action through the wick to the evaporator end, thus closing the loop.
Heat-pipes have been used commercially for decades as a means of xe2x80x98passivelyxe2x80x99 removing excess heat from critical, confined areas and transporting it to a remote condenser (or radiator). Heat pipes are used in spacecraft, for instance, to remove power from internal electronic components, and transport that power to radiators on the outside of the spacecraft. They have also been applied to the consumer electronics (computer) industry to remove the heat generated by high-powered processors. Heat pipes have recently become very affordable, due to major advances in automated manufacturing techniques, and are available in a variety of shapes and dimensions, wick-types, and cooling fluids. The same technology has also been applied to xe2x80x98plates,xe2x80x99 whereby heatpipes are embedded in thin pads, with a single condenser attachment point.
Due to the enormous latent heat of vaporization of some fluids, the heat-removing capacity of heat pipes is enormous; easily 10,000 times that of solid copper rods of equal dimensions. In addition, the xcex94T (xe2x80x98delta-Txe2x80x99) or temperature difference between a power source and the condenser can be as low as a few degrees while for a similarly dimensioned copper rod the xcex94T would be much higher. This condition is especially true when heat exchange is limited primarily to conduction, as it is when the power source is being operated in ultra high vacuum environments. (Radiation and convection are the other means of thermodynamic exchange, and only radiation and conduction play a part in vacuum thermal exchange.)
The application of proven heatpipe technology to terrestrial vacuum environments is the focus of this invention. The present invention describes a passive means of removing large amounts of power (hundreds of Watts), inexpensively, simply, and effectively, without compromising the cleanliness of the vacuum chamber. The important aspects of the invention are:
I. A heatpipe that extends from within the walls of a vacuum vessel, wherein a heat generating source is located, to the outside of the vacuum vessel, wherein a cooling means is available. This heatpipe is therefore referred to as a xe2x80x98vacuum feedthrough heatpipe.xe2x80x99
II. A means of attaching the heat generating source to the heat pipe with contacts of high thermal-conductivity (pieces that clamp onto the heat-pipe, or that are bonded, soldered, brazed, or otherwise attached with high thermal-conductivity means);
III. A choice of materials and coatings that permit optimal operation within the UHV environment (such as nickel plating on the copper heat pipe, and highly polished aluminum clamp pieces. Such low-absorptivity finishes are necessary in order to minimize radiative coupling to the environment);
IV. A means of joining the heatpipe to a suitable vacuum feed-through, utilizing brazed, welded, soldered, or bonded vacuum seals; and,
V. Cooling the condenser-end of the heat-pipe (outside of vacuum) using either convection (forced or natural), or conduction (such as a coil of water or other heat-transfer medium, or a thermo-electric cooler unit). The temperature of the condenser can thusly be accurately controlled in order to provide a range of operating temperatures of the evaporator (the xcex94T remains constant for a given source-power).
VI. An articulated assembly formed of a plurality of arms joined by adjustable elbow assemblies, wherein each arm comprises a heatpipe, and the condenser end of one heatpipe is joined to the evaporator end of the next heatpipe.
This device could be used anywhere it is necessary to remove xe2x80x98wastexe2x80x99 heat from within a vacuum vessel or chamber. Without special means of removing heat from vacuum chambers, heat-producing processes will become very hot during operation. Use of this device will be very advantageous when contamination control of the vacuum vessel is critical, or when conventional cooling means do not have sufficient capacity to cool the heat-source.
The conventional means of removing heat from within vacuum chambers (wafer fabrication chambers, deposition chambers, or powered instruments, for example) are:
a) Solid copper rods for which there is generally a large and uncontrollable temperature difference, xcex94T. The large thermal mass of copper also requires a long time to equilibrate.
b) Liquid or gaseous cooling coils for which plumbing and fittings inside the vacuum vessel are typically required. These are often undesirable, in that the cooling fluid may escape into the vacuum chamber in time, due to thermal or mechanical cycling of the plumbing fixtures and connections. Also, water is typically poured wastefully down the drain to avoid the high cost of recycling heat exchangers.
The vacuum feed-through heat-pipe assembly has no moving parts within the vacuum chamber, and therefore has extremely long life. It is a completely sealed unit, fabricated of ultra-high vacuum-compatible materials, thereby providing a long lifetime of extremely clean operation. The thermal mass of the system is very low, allowing for rapid response to power changes. Finally, temperature control of the condenser end allows for accurate control of the source temperature, since the temperature drop across the heatpipe is constant for a given source power.